Method for content-aware redirection and content renaming

ABSTRACT

The present invention is directed to mechanisms for content-aware redirection and content exchange/content discovery that permit a request for content to be redirected to a particular advantageous server that can serve the content.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to content distribution inpacket-switched networks.

[0002] Packet-switched networks, such as networks based on the TCP/IPprotocol suite, can be utilized to distribute a rich array of digitalcontent to a variety of different client applications. The most popularapplications on the Internet today are browsing applications forsearching the World Wide Web, e.g. Netscape Navigator or MicrosoftInternet Explorer, which utilize the HyperText Transfer Protocol (HTTP)to retrieve documents written in the HyperText Markup Language (HTML)along with embedded content. See, e.g., R. Fielding et al., “HypertextTransfer Protocol—HTTP/1.1,” IETF Network Working Group, RFC 2616(1999), which is incorporated by reference herein. Other protocols fordelivering data such as streaming media across the Internet include theReal Time Streaming Protocol (RTSP). See, e.g., H. Schulzrinne et al.,“Real Time Streaming Protocol (RTSP),” IETF Network Working Group, RFC2326 (April 1998), which is incorporated by reference herein. Resourceson the Internet, such as HTML documents or multimedia content, areidentified by Uniform Resource Identifiers (URIs). See, e.g., T.Berners-Lee et al., “Uniform Resource Identifiers (URI): GenericSyntax,” IETF Network Working Group, RFC 2396 (August 1998), which isincorporated by reference herein. URIs can be expressed by arepresentation of their locationdependent network access mechanism, i.e.as a Uniform Resource Locator (URL) (e.g.“http://www.xyz.com/dir/document.html”), or by a persistent namereferred to as a Uniform Resource Name (URN).

[0003] It is often advantageous when distributing content across apacket-switched network to divide the duty of answering content requestsamong a plurality of geographically dispersed servers. Companies such asAkamai Technologies, Digital Island, AT&T and Adero provideservices—referred to in the art as “content distribution”services—utilizing architectures which dynamically redirect contentrequests to a cache advantageously situated closer to the client issuingthe request. Such network architectures are referred to hereingenerically as “content distribution networks” or “CDNs” for short. Inits simplest form, content distribution networks consist of originservers and edge servers. Clients connect to edge servers to requestcontent. Requested content may already be in the edge server that theclient connect to (for example if all of the edges are pre-populatedwith all of the content), or the edge server in question might fetch thecontent from the origin server on-demand if it does not already have therequested content. These two extremes, namely complete pre-population ofthe edges and on-demand loading of the edges, is clearly suboptimal interms of storage and latency respectively. This is particularly true inthe case of high quality streaming content where storing all of thecontent in all of the edge servers will not be feasible. At the sametime if say a particular large piece of digital content, e.g. a movie,is already at an edge server, a new client requesting the same moviemight potentially be best served from the same edge server.

SUMMARY OF INVENTION

[0004] The present invention is directed to mechanisms for content-awareredirection and content exchange/content discovery that permit a requestfor content to be redirected to a particular advantageous server thatcan serve the content. In accordance with an embodiment of theinvention, the content-aware redirection mechanism roughly consists of afront-end and a back-end. The front-end makes use of the requestedcontent to redirect a request to an edge server where the content mightalready be present or an edge that should request the content from theorigin. The back-end takes part in a content exchange/content discoveryprocess to determine where content is currently located. The requestedcontent can advantageously be rewritten during the redirection processto not require the name of the requested and served object to be thesame. Content renaming can be utilized for example to efficiently mapdifferent content names to the same piece of stored content.

[0005] These and other advantages of the invention will be apparent tothose of ordinary skill in the art by reference to the followingdetailed description and the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0006]FIG. 1 is a conceptual representation of a content managementarchitecture.

[0007]FIG. 2 is a conceptual representation of content redirection andcontent discovery in a network, in accordance with an embodiment of thepresent invention.

[0008]FIG. 3 is a conceptual representation of content redirectionutilizing protocol redirect.

[0009]FIG. 4 is a conceptual representation of content redirectionutilizing a dynamic helper file.

[0010]FIG. 5 through 9 illustrate different architectural options forcontent discovery, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

[0011]FIG. 1 is a conceptual representation of a content managementarchitecture.

[0012] Content can be distributed to clients from either origin servers,e.g. 161, 162, or from clusters of edge servers, e.g. 151, 152, . . .155. It is advantageous to have a content manager 110 which is able toselectively pre-populate some of the edge servers with content based onvarious factors, such as a negotiated service agreement, load, theparticular service type, other policies, etc. In particular, forexample, for high-quality streaming of media, it is desirable not tohave all of the content populating all of the edge server clusters. Inthis type of environment it becomes crucial for a client to connect toan edge server that already has the content it is requesting. Thepresent invention is directed to various mechanisms which facilitateeffective content management.

[0013]FIG. 2 is a conceptual representation of content redirection andcontent discovery in a network, in accordance with an embodiment of thepresent invention. The system, roughly speaking consists of two parts: afront end responsible for redirecting clients and a back end thatdetermines where the client should be redirected. A network 200distributes content from multiple edge and origin servers to clients,e.g. client 280. The present invention is not limited to a particularcontent distribution architecture, although an advantageous architecturefor the distribution of streaming content is described in co-pendingcommonly-assigned U.S. patent application, “Network Based ReplayPortal,” Ser. No. 09/726,576, filed on Dec. 1, 2000, which isincorporated by reference herein. At step 201, a media client 280consults a local domain name system (DNS) server 211 with a URL for theparticular content it seeks. The DNS server 211, at step 202, resolvesthe URL to a redirect server 220. The redirect server 220 queries amapping service 230 responsible for determining where content is locatedin the system. The mapping service, as further described below, cancomprise one or more mapping servers which receive updates from originservers 261, . . . 262 and from edge servers 251, . . . 255. At step204, the redirect server 220 redirects the client to an advantageousedge (or origin) server. At step 205, the client 280 requests thecontent from the media server.

[0014] Redirection Mechanisms

[0015] There are at least two places where the redirection can takeplace. For example, and without limitation, streaming media over an IPnetwork typically involves first making a selection from an HTML webpage. As a result of the selection, a helper file is downloaded and amedia player application is started. The helper file contains astreaming URL (or URLs) which the player then uses to connect to therelevant media server by means of a streaming control protocol.

[0016] The first method of redirection involve dynamically generatingthe helper file with a URL (or URLs) containing the hostname (or IPaddress) of the edge server that the client should be connecting to.

[0017] The second method of redirection makes use of explicitredirection that is present in most streaming control protocols(including RTSP, HTTP and MMS (in version 7.0)). In this case the mediaclient connects to a redirecting media server. This media server neverserves up content but always redirects the client by means of thecontrol protocol to the appropriate edge server.

[0018] Note the proposed solution also enables an additional benefitbeyond finding the appropriate edge server: The requested content(object) is taken into account in making the redirection decision. Theresult of the redirection is a new URL which contains a new hostname (ormore likely the IP address) of the selected edge server as well as theselected object. This allows the opportunity to also remap the requestedobject during the redirection process. The implication of this is thatname of the object that a user selects and the name of the object it isactually served need not be the same. This property can be exploited ina number of ways. For example a CDN customer (i.e. a content provider)can use its own naming convention which gets mapped onto a namingconvention within the CDN which is more efficient for the CDN provider.(E.g. a CDN provider might determine that the a piece of contentprovided by two different content providers are really the same piece ofcontent (such as a movie for example) and therefore choose to exploitthat within the CDN to have two different customer names map to the samepiece of stored content.)

[0019]FIG. 3 and 4 illustrate the two different methods of redirection.FIG. 3 is a conceptual representation of media redirection utilizing aprotocol-level redirect, specifically in the context of the RTSPprotocol. At step 301, a media client 380 has a URL, e.g.“rtsp://sr.target25.com/clip.rm”. At step 302, the domain name systemresolves the domain name “sr.target25.com” to any of the streamingredirect servers 320. At step 303, the media client 280 connects to thechosen streaming redirect server 320 with the URL“rtsp://sr.target25.com/clip.rm”. At step 304, the streaming redirectserver 320 decides on an “appropriate” content server for this request,for example redirecting the client to an edge server 351 with the URL“rtsp://mec10.att.net/att/clip.rm”. The IP address of the edge server351 can be utilized to prevent a DNS lookup. Then, at step 305, themedia client 380 connects to the media edge cluster to stream thedesired content. The media edge cluster 351 may already have the contentin a cache or may obtain the content from a media origin server 361.

[0020] Protocol-level redirection does not rely on any standardizednaming convention. A URL such as“rtsp://sr_rtsp.target25.com/balloon.rm” can map to“rtsp://real.atticds.speedera.net/real.atticds/balloon.rm” or to“rtsp://live-atticds.com/balloon.rm”, for example with equalprobability. Where a movie URL such as“rtsp://sr.att.com/bb/the_messanger” is requested, the URL could bemapped to “rtsp://mec5.icds.att.net/movies?id=1011” assuming that thecontent is already on the server cluster “mec5” or could be mapped to“rtsp://mec5.icdns.att.net/bb/the_messanger?url=rtsp://mos3.icds.att.net/movies?id=1011”where the movie is still on a central server “mos3” but it is desired tostream the movie from server cluster “mec5”.

[0021]FIG. 4 is a conceptual representation of content redirectionutilizing a dynamic helper file. At step 401, a user utilizing a webclient 490 selects a media clip from a web page on a web server 495. Theweb server 495, at step 402, dynamically generates a helper file (e.g.,a “.ram” or “.asx” file) with the appropriate URL, e.g.,“mms://mec10.att.net/clip.asf”. At step 403, the web client 490 invokesthe media player 485, which contacts the domain name system at step 404to resolves “mec10.att.net”. Alternatively, the URL could be expressedwith an IP address to avoid the DNS lookup. Then, at step 405, the mediaplayer 485 connects to a media edge cluster 451 to stream the desiredcontent. The media edge cluster 451 may already have the content in acache or may obtain the content from a media origin server 461.

[0022] This method of redirection again does not rely on anystandardized naming conventions and can redirect between differentprotocols. For example, a URL of“http://www.target25.com/cgi-bin/getasx.asx?url=balloon.asx” can bemapped so that it returns an asx file with“href=http://httpmode.atticds.com/commercial/balloon.asf” or“href=mms://wm.atticds.speedera.net/wm.atticds/balloon.asf” with forexample equal probability.

[0023] Note that it is not possible to do content aware redirection withother known redirection methods, in particular, DNS-based redirection.The reason is that DNS resolution resolves a DNS hostname to an IPaddress. The content part of a URL is therefore not taken into account.It is in principle possible to somehow “encode” the content into thehost name and therefore overload the DNS system to be content-aware.There would however be a number of (known) problems with such asolution:

[0024] Load on the DNS system would dramatically increase as the systemwould be used in a way that it was not designed to be used.

[0025] By design the decision making would be more course grainedbecause of DNS caching/time-to-live, no knowledge of the clientrequesting IP address and the fact that many clients might be hiddenbehind a single DNS query.

[0026] With DNS based redirection schemes it is also impossible toperform any mapping of the requested object name as it is not availablewithin the DNS query.

[0027] Mapping Service

[0028] The decision as to where a media client should be redirected totypically involves many inputs. This might include load in the network,load at edge servers, policy, locality of client to CDN nodes, networkcharacteristics between client and CDN nodes etc. The key criteria weare concerned with in this writeup however is the content that is beingrequested and where this currently resides in the CDN. Or more generallyhow that content should be obtained. For example, for live content, thedecision might be to serve it from a particular edge server because ofits locality, and the way for the edge server to obtain the contentmight be to join an application level streaming distribution tree.

[0029] One way in which the backend could be realized is to have allcomponents (origin servers, edge servers, streaming redirectors, etc)take part in a content exchange/content discovery process. Asillustrated by FIG. 2, origin and edge servers advertise the fact thatthey have a particular piece of content to a mapping service 230. When aredirector 220 receives a request for content it in turn consults themapping service 230 to find out if and where the content is availableand redirects the media client appropriately.

[0030] Thus, the primary function of the mapping service is to returnthe location of a piece of content, identified for example by a URN. Inresponse to a query, the mapping service is responsible for returning alist of URLs specifying the servers on which the content may be found. Afull query might look like this, in the context of a mapping service fortelevision broadcast content:

[0031] <channel_name; brand; distributor; region; time;requestor_location>

[0032] The mapping service without limitation can be modeled as a huge,singletable database containing the following fields:

[0033] Time, Channel Name, Brand, Distributor, Region, Portal

[0034] In this naive approach, there is an entry in the database forevery piece of content on the content network, regardless of whetherthat piece of content is unique or replicated. In other words, if thesame piece of content is mirrored in twenty locations, there will betwenty distinct records in this database.

[0035] The mapping service, in accordance with a preferred embodiment ofthe invention, can accept two types of message: queries and updates.Queries ask the mapping service to locate a piece of content, identifiedby its URN. Updates allow portals to add content to the mapping service,delete it, or change certain attributes pertaining to a piece ofcontent. There are a number of implementation approaches for the mappingservice, which are listed below. As shown below, the most importantissues to consider when designing a mapping service are the size of thedatabase, the search time and the quantity of traffic.

[0036] 1. Centralized Database. In this solution, updates and queriesare directed from the portals to a single, centralized mapping server,as illustrated by FIG. 5. To speed local searches, a “Local MappingServer” (LMS) can optionally be placed in each neighborhood as anintermediary. The Local Mapping Server serves the purpose of aggregatinglocal content, as well as performing all communication with the CentralMapping Server (otherwise referred to herein as a “Global MappingServer” (GMS)). Conceptually, this is the most straightforwardimplementation of the mapping service. This solution has thedisadvantage of being relatively vulnerable to database failure; if theserver were to go down or become unreachable, a large portion of thefunctionality would become unavailable for searching.

[0037] 2. “Gnutella”net/Multicast Distributed Database. In thisconfiguration, illustrated by FIG. 6, each portal (or group of portals,represented by a Local Mapping Server) maintains a database of its ownstored content. There are no update messages transmitted between thesenodes. When one node wishes to query the database, a query is broadcastto all nodes (through a network flooding scheme, or through multicast.)Any nodes containing the content then respond directly to the nodeinitiating the query.

[0038] Unlike the singledatabase solution, this solution has theadvantage of being relatively invulnerable to database failure; if oneof the many nodes fails, only the content stored in that neighborhoodbecomes unavailable to the rest of the world. Database size is no longeran issue, as databases are maintained locally. Search times are lowerfor each local database, as these databases will be much smaller than alarge amalgamated database (although the process of disseminatingqueries could potentially add a great deal to the response time.)Finally, if the queries are distributed along paths that resemble thenetwork topology, it is likely that the earliest responses will comefrom those nodes “closest” to the querying node. The primarydisadvantage to this solution is the large amount of query traffic,which would be broadcast to all clients; this flooding could potentiallyoverwhelm the portals. Other problems include the lack of a “guarantee”of query failure—if no responses are received within a specified timeperiod, querying nodes must simply assume that the search failed. By thesame token, it is also possible that some searches will result in toomany responses, temporarily overloading the querying node. Large amountsof broadcast query traffic would make this solution unworkable. As querymessages are triggered by individual clients (viewers), it is possiblethat query traffic could be relatively large, possibly hundreds ofthousands of queries per second. As this traffic is broadcast to allnodes, nodes might be unable to handle this enormous flood of queries.Although there might exist some mechanisms for reducing the quantity ofquery traffic (such as limiting the TTL of query requests) but thesemight not solve the problem.

[0039] 3. Multiple Partitioning (Partitioned byChannel/Time/Distributor/etc.) Database. As illustrated by FIG. 7, thisscheme improves on the scalability of the singledatabase approach, bypartitioning the database into many smaller databases. Each of thesesubdatabases contains records associated with a given channel, time ordistributor (for example.) When a portal wishes to perform a query, oneof these subdatabases is chosen using information from the query URN.For instance, if the query URN contains the following information:

[0040] <ABC;WABC;comcast;new_jersey;10:30PM>Then the querying node mightaddress the query to the subdatabase server responsible for recordsrelating to the channel “ABC”, to the server responsible for theaffiliate “WABC”, or to the server responsible for distributor “comcast”(etc.) The actual address of the servers might be calculated simply bygenerating a domain name (e.g. ABC.prism.att.com, WABC.prism.att.com,comcast.prism.att.com.).

[0041] The decision on which database to contact would depend on how thesub-databases are partitioned. If information is partitioned accordingto only one parameter (channel, for instance), then the querying node'sdecision would be straightforward. If the partitioning was based onmultiple parameters—if, for instance, there existed both a “comcast”database and an “ABC” database—then the querying node would have tochoose which database to contact. If data is to be partitioned based onmultiple parameters—for example, if we do have both an “ABC” databaseand a “comcast” database—then the contents of the “comcast” databasewould need to substantially overlap the contents of the “ABC” database.This could lead to a great deal of database replication, and alsorequires that updates received at one database (“comcast” for instance)would need to be propagated to all other relevant databases (“ABC” and“WABC”.)

[0042] This solution is potentially an improvement on earlier modelswith regards to scaling in that it does reduce the quantity of querytraffic handled by individual databases. However, it does notnecessarily reduce the traffic in a uniform way.

[0043] Whether we partition the databases by channel name or any otherparameter, there is no guarantee that query traffic will be evenlydistributed across the resulting subdatabases. Since there will be sucha high degree of database replication under this scheme anyway, it mightalmost make more sense if we simply replicated the full database manytimes (as illustrated below), and asked querying nodes to pick a serverat random from a list. This way, we could at least guarantee a certainamount of uniformity.

[0044] 4. Replicated Central Databases. One of the most desirablefeatures of a distributed database is the ability to redistributedynamically, based on changes in load and the number of records. If itis assumed that one of the challenges will lie in regulating the numberof queries, then one could use the simple mechanism mentioned in theprevious paragraph: simply replicate the full database many times, andcreate a mechanism for distributing queries amongst the clones, asillustrated by FIG. 8. This approach would require a mechanism forpropagating update traffic to all of the databases.

[0045] 5. Replicated Local Databases (“Cnutella”Net approach). Anothervariation on the distribution of functionality would be for all portalswithin a neighborhood to constantly update each other about their storedcontent, as illustrated by FIG. 9. Each portal would therefore maintaina complete database of content available within its own neighborhood. Tolocate content that is not in the local neighborhood, this schemedesignates a “gateway” portal within each neighborhood to take part in asimilar distribution of available content with gateway portals fromother neighborhoods. The gateway portal would be responsible foraggregating the reports of content available within its ownneighborhood, transmitting that information to all other neighborhoods,and collecting reports back from other neighborhoods. In this scheme,the gateway portal represents the neighborhood at the interneighborhoodlevel and individual portals within the neighborhood are not visiblefrom the outside during this part of the content discovery process.

[0046] In this scheme a query would be handled as follows: Uponreceiving or initiating a query, a portal would first check its localdatabase, which would contain a full record of all content to be foundwithin the neighborhood. If the query item were not found, the portalwould then send a request to the neighborhood's gateway portal, whichwould then look the item up in its much larger “global” database.

[0047] This scheme could be repeated on larger scales, as well. Multipledomains can be linked in much the same way that different neighborhoodsare linked in the above model. Again a designated node (this time fromamong the interneighborhood participants) would exchange informationwith peers in other domains. In this case, in addition to aggregatingthe reported content available within the domain, the designated portalwould be responsible for implementing any policy filtering that might berequired for exchange of content between domains. The advantage of thisscheme is that the same basic scheme can be used at different levels inthe hierarchy. Being completely distributed the scheme is potentiallyvery robust against node failures. For the common case this schemelocalize queries (the rate of which is user dependent) at the expense ofhaving to distribute updates (the rate of which can be largelycontrolled by the system) throughout the neighborhood.

[0048] The major disadvantage to this scheme is that it might be toocomplicated for a local scheme, while an interdomain mechanism might bebetter served by a query-based solution. While potentially more robustthis scheme is a lot more complicated than a simple centralizedapproach. A major worry in this configuration is that the individualdatabases might get out of sync with each other. This could occur if anumber of update messages are destroyed. Once this occurred, it would bea very difficult situation to recover from, and could result inimportant content become inaccessible.

[0049] Another possibility would be to sort the database according tothe one parameter that is unique in streaming content: time. If recordsare sorted by time, they can be broken up across several databases andqueries directed properly based on the time requested. If query trafficreached uncomfortably high levels on any one server, that server coulddynamically repartition, dumping some of its more popular records ontoanother server. With this approach, a mechanism is required for mappingrequests to the correct server, even as records were moved.

[0050] Mapping Protocol

[0051] The following is a description of an advantageous mappingprotocol, which the inventors have named the “URI mapping protocol”(UMP). The purpose of UMP is to map one URI to another, e.g. it can mapa URN to a URL as part of the content discovery mechanism describedabove. The protocol could however be used in any generic URI mappingapplication. Similar to HTTP, RTSP and SIP, the UMP protocol is textbased. It also attempts to rouse many of the header fields defined bythese protocols.

[0052] The following provides a framework in which a more detailedprotocol specification can be developed by one of ordinary skill in theart depending on the requirements and understanding of the problemspace. In particular, in a distributed realization of the protocol, itwill be necessary to add messages (and other support) to build thedistribution network. There description does not specifically addressany security or authentication issues, although known ideas from HTTPcan clearly be reused.

[0053] This protocol can run over either a reliable transport protocol(e.g. TCP) or an unrealiable transport protocol (e.g. UDP). Followingthe example of RTSP and SIP a retransmission scheme is used only in thecase where an unreliable transport is used. Similarly, since IP levelfragmentation is undesireable, it should be required (like SIP) that UDPdatagrams fit in one MTU if it is known or in 1500 bytes which isconsidered a reasonable default MTU size. Again following the SIPexample, more compact representation of encodings can be used to reducethe per message length. For UMP over UDP, it is required that a responsethat would not fit in an MTU be truncated and sent with an appropriateerror indication. Even though it is not the complete intended message,the truncated part of the message should be a properly formattedmessage. For example, a query that resulted in 20 mappings should return15 complete mappings, assuming that is all that can fit in the MTU,rather than 15.5 mappings, with an error indication that all resultscould not be returned. Alternatively, a response to a UDP received querycan be sent back over TCP, if allowed by the client.

[0054] The default operation for UMP is a “request-response” typeinteraction where every request message is acknowledged by the recipientby means of a response message. Pipelining of requests are allowed andin this case the order of responses do not necessarily have to match theorder or requests. Receipt of the response message by the requestorterminates this transaction (indicated by the transaction ID in themessage pair). In the absense of other mechanisms, failure to receive aresponse after a reasonable timeout can be used by UMP to triggerretransmission in the case where UMP runs over UDP. An alternative is tomake use of some reliable transport layer between UMP and UDP. In UMPthere are two exceptions to this default one-request-one-response formof interaction:

[0055] In a distributed query operation, the first recipient of thequery might be able to resolve it (i.e. produce a response message), butit will also pass the request on to its neighbors in the distributionnetwork. These neighbors in turn might be capable of resolving the query(and sending it back towards the recipient) and will similarly pass onthe request to their neighbors. In this mode of operation, the requestor(and nodes along the distribution network) should therefore be capableof processing multiple responses for each request. To accomodate UDPbased implementations which might rely on the response for itsretransmission scheme, a node should send back a response to theprevious hop if it is forwarding the request to another node. Thisshould be done even if the node in question was unable to resolve thequery. If the node was able to resolve the query, the provisionalresponse should contain these responses. Such a provisional responseshould indicate that it is not a final answer. The default case would beto use the provisional response for UDP but not for TCP, but the clientis allowed to overide the default.

[0056] In a distributed update operation, e.g. by using nativemulticast, the requester can indicate that it does not require anacknowledgement on its request. Since reliability can not be guaranteedin this mode of operation it is assumed that consistency will beprovided by some other means, e.g. periodic refreshes and time-to-livevalues associated with mapping entries, or by making use of reliablemulticast.

[0057] It is also advantageous to provide an OPTIONS message pair aswell which will establish connectivity between communicating entities,telling the other end what type of node it is (e.g. client/server versusdistributed operation transport protocols it can use, etc.).

[0058] The use of one URI per Query-Request and one URI mapping (e.g.URN to URL) per Update-Request simplifies the protocol. Use of multipleURI in Query-Request does not appear that compelling and it doescomplicate processing (e.g. what happens when a local mapping server canresolve some of the URIs locally but need to contact another entity toresolve the rest). For Update-Request the usefulness of multiple URIsseems more compelling. However, in this case pipelining the updates inone transport level message will work well enough albeit moreinefficient. If this prove too limiting in practice, it is alwayspossible to extend the protocol later on to accomodate multiple entries.

[0059] The following is a specification for the query messages, inaccordance with a preferred emb

[0060] Query-Request: ------------- R QUERY <query-URI (URN)>UMP/1.0 RVia: <list

[0061] Query-Response: -------------- R UMP/1.0 Status-CodeReason-Phrase R Via: <1

[0062] Note that “FromURI” has to be in response so that a querier knowwhat the mapping is even if th

[0063] The following is a specification for the update messages, inaccordance with a preferred em

[0064] Update-Request: --------------- R UPDATE <update-URI(URN)>UMP/1.0 R Via: <1

[0065] Update-Response: --------------- R UMP/1.0 Status-CodeReason-Phrase R Via: <

[0066] Note that the “update-URI” should be fully qualified with norange specification.

[0067] The “TransactionID” should be an opaque string of at least 8octets. The “TransactionlD” must be unique for every unique request. Itcan, without limitation, have a random component to it and/or can beglobally unique when considered together with the sender's hostname.

[0068] It is also advantageous to add the following new status code:

[0069] New Status-Code Reason-Phrases =========================32====230 Provisiona

[0070] The following are examples of the use of the above protocol forthree scenarios: (1) where there is a centralized local mapping server(LMS) with a centralized global mapping server (GMS); (2) Distributed(replicated) LMS/distributed (replicated) GMS; and (3) Distributed(partitioned) LMS/distributed (partitioned) GMS.

[0071] Centralized LMS with centralized GMS. Consider where there is aninitial update from a port

[0072] Request (from portal11 to 1 ms234):----------------------------------- UPDAT

[0073] The LMS will then send a similar update to the GMS (it might beimmediate or it might wait for a

[0074] Request (from 1 ms234 to gms2): -----------------------------UPDATE stv:<abc

[0075] Suppose a client request for stv:<abc;;;>is received by a portalin the same neigborhood as

[0076] Request (from portal12 to lms234):--------------------------------- QUERY s

[0077] Suppose a client request for stv:<abc;;;>is received by a portalin a different neighborhood

[0078] Request (from portal31 to 1 ms456):--------------------------------- QUERY st

[0079] In this example, RTSP URLs are never visible outside the localneighborhood and a query therefo

[0080] 2. Distributed (replicated) LMS/distributed (replicated) GMS(gnutella-like updates). Assume

[0081] Request (from portal11 to each of its neighbors in the network):-----------

[0082] At this point the update is done as far as portall 1 isconcerned. Each of the neighbors that has

[0083] Request (from portal13 to each of its neighbors in the network)----------

[0084] This process continues until all portals in the neighborhood havereceived the update. The des

[0085] Location: ump://portal15.att.net

[0086] This will allow the same hiding of the details of any particularneighborhood as in the previous

[0087] Any query received for stv:<abc;;;>in portal11's neighborhoodwill be resolved locally by th

[0088] Request (from portal31 to portal39):--------------------------------- QUERY

[0089] As before portal31 will then proceed to query portal15:

[0090] Request (from portal31 to portal15)--------------------------------- QUERY s

[0091] What is interesting in this approach is how portals know at whatlevel(s) of a hierarchy they sho

[0092] 3. Distributed (partitioned) LMS/distributed (partitioned) GMS.In this approach there are no updates. Instead queries are broadcastgnutella style through an overlay network. We assume that similar to theprevious section a distribution network has already been established andthat it is organized into neighborhoods. Designated nodes in eachneighborhood form a higher level group by similarly having adistribution network amongst themselves. The “RegionTTL” field is usedto determine the scope of a query.

[0093] As before, assume that portall 1 carriesstv:<abc;wabc;comcast;summit.nj>. A client reques portal13 to each ofits neighbors: --------------------------------- QUERY s

[0094] Negative acknowledgements are not relayed back to the originalrequestor. A designated node

[0095] A query from a different neighborhood will be handled in similarfashion and assuming the scope of the query is higher than 1 willeventually via the higher level network end up in the neighborhood whereportall 1 resides. portall 1 will respond in exactly the same way asabove so that the requesting portal will end up with the URL forportal11. (In this case there is no LMS in the loop.)

[0096] Note that in the case where multiple responses are possible, animplementation (at the initial requester side) must be capable ofreceiving (and discarding) reponses (long) after it might have cleanedup any state associated with the request. Other solutions to thisproblem involve the first upstream node maintaining state so theresponses can be merged before being sent to the requester andsubsequent responses discarded.

[0097] It should be noted that it would be advantageous to includesomething in the protocol to indicate which protocol to use forinteraction. It might be preferable to have a PortallD as additionalinformation (e.g. this could simplify the index operation when an updateis received). It may be preferable to ensure that redirects (e.g. fromLMS to GMS back to LMS to GMS, etc.) will not occur and that when theydo occur that the situation will not be disastrous. Also, the via fieldswill prevent loops from forming but will not prevent messages from beingprocessed many times by the same node in the distributed cases. Thismight be addressed by requiring the distribution network to be a tree orby having nodes cache the transaction ids of recently seen messages (asin Gnutella). Finally, it should be noted that it is possible to do awaywith query response messages and only have updates, which can be eithersolicited or unsolicited.

[0098] The foregoing Detailed Description is to be understood as beingin every respect illustrative and exemplary, but not restrictive, andthe scope of the invention disclosed herein is not to be determined fromthe Detailed Description, but rather from the claims as interpretedaccording to the full breadth permitted by the patent laws. It is to beunderstood that the embodiments shown and described herein are onlyillustrative of the principles of the present invention and that variousmodifications may be implemented by those skilled in the art withoutdeparting from the scope and spirit of the invention. For example, thedetailed description has been presented in the context of particularprotocols such as RTSP and HTTP; however, the principles of the presentinvention could be extended to other protocols and content distributionarchitectures. Such an extension could be readily implemented by one ofordinary skill in the art given the above disclosure.

1. A method for distributing content in a packet-switched networkcomprising the steps of: receiving from a client a request for contentidentified by a resource identifier; querying a mapping service usingthe resource identifier of the content; receiving a list of servers inthe network that store the content identified by the resourceidentifier; and redirecting the client to one of the servers using asecond resource identifier.
 2. The invention of claim 1 wherein theclient is redirected using protocol-based redirection.
 3. The inventionof claim 1 wherein the client is redirected using a helper file.
 4. Theinvention of claim 1 wherein the resource identifier is a URN and thesecond resource identifier is a URL.
 5. A method for distributingcontent in a packet-switched network comprising the steps of: storing ina database a list of servers in the network that store contentidentified by a resource identifier; updating the database as contentstored on the servers change; responding to queries requesting contentidentified by a resource identifier with the list of servers that storethe content, wherein the list of servers can be used to redirect clientsto one of the servers.
 6. The invention of claim 5 wherein the databasehas a centralized mapping server.
 7. The invention of claim 6 whereinthe database is updated in response to update messages received from theservers.
 8. The invention of claim 5 wherein the database is distributedamong servers in the network.
 9. The invention of claim 8 whereinupdates to the database are not broadcast to the servers and whereinqueries are broadcast to the servers.